swig/Doc/Devel/Javascript/V8_CodeGeneratorSpecification.md

Javascript: Specification of a Code Generator for V8

The aim of this is to evolve a specification for a code generator.

Top Level structure

The generated code consists of the following blocks:

<HELPER_FUNCTIONS>

<INCLUDES>

<CLASS_TEMPLATES>

<FUNCTION_WRAPPERS>

<INITIALIZER>

• HELPER_FUNCTIONS: static, from swg-file
• INCLUDES: static, module property
• CLASS_TEMPLATES: dynamically growing, on class declarations
• FUNCTION_WRAPPERS: dynamically growing, on method declarations
• INITIALIZER: dynamically growing, aggregates everything (to be specified in more detail)

INCLUDES

#include <v8.h>

<USER_DEFINED_INCLUDES>

USER_DEFINED_INCLUDES: a module property

CLASS_TEMPLATES

Static references to class templates which are (should be) read-only and can be reused.

v8::Persistent<v8::FunctionTemplate> SWIGV8_$CLASSNAME;

Notes:

• it is very important to consider namespaces from the beginning. CLASSNAME should be fully canonical, e.g., foo_bar_MyClass for foo::bar::MyClass
• namespaces do not need a function template, as they will not be instantiated

FUNCTION_WRAPPERS

There are different types of function wrappers:

• Static Functions (global/namespace/class)
• Constructors / Destructors
• Getters / Settters
• Member Functions

Static Functions

TODO

Constructors

v8::Handle<v8::Value> $CLASSNAME_new(const v8::Arguments& args) {
    v8::HandleScope scope;
    
    // retrieve the instance
    v8::Handle<v8::Object> self = args.Holder();
    
    // TODO: declare arguments

    //convert JS arguments to C++
    // TODO: apply input typemaps

    $CLASS_LVAL* ptr = new $CLASS_LVAL($ARGS);
    self->SetInternalField(0, v8::External::New(ptr));
    
    return self;        
}

• $CLASS_LVAL: should be the canonical name of the class, e.g. ns1::ns2::MyClass
• $ARGS: arguments should be declared at the beginning and checked and set in the input typemap block

Destructors

TODO

Getters

v8::Handle<v8::Value> $CLASSNAME_get$VARNAME(v8::Local<v8::String> property, const v8::AccessorInfo& info) {
    v8::HandleScope scope;

    // retrieve pointer to C++-this
    $CLASS_LVAL* self = SWIGV8_UnwrapThisPointer<$CLASS_LVAL>(info.Holder());
    $RET_LVAL retval = self->$VARNAME;
    
    v8::Handle<v8::Value> ret = <output_mapping(retval)>;
    return scope.Close(ret);
}

• TODO: output typemapping

Setters

void $CLASSNAME_set$VARNAME(v8::Local<v8::String> property, v8::Local<v8::Value> value, const v8::AccessorInfo& info) {
    v8::HandleScope scope;

    // retrieve pointer to this
    $CLASS_LVAL* self = SWIGV8_UnwrapThisPointer<$CLASS_LVAL>(info.Holder());

    // TODO: declare input arg
    
    // map java-script type to C++ type    
    self->$VARNAME = <input_typemapping>;

}

TODO:

• input type mapping should be addressed in extra step, together with type check

Member functions

v8::Handle<v8::Value> $CLASSNAME_$FUNCTIONNAME(const v8::Arguments& args)
{
    v8::HandleScope scope;

    $CLASS_LVAL* self = SWIGV8_UnwrapThisPointer<$CLASS_LVAL>(args.Holder());

    // TODO: declare input args

    //convert JS arguments to C++
    // TODO: input typemappings and type checking

    //call C++ method
    $RET_LTYPE result = self->$FUNCTIONNAME($ARGS);

    //convert C++ JS arguments to C++
    v8::Handle<v8::Value> ret = <output_typemapping>;

    return scope.Close(ret);
}

• if the function does not have a return value, return v8::Undefined

Initializer

void $MODULENAME_Initialize(v8::Handle<v8::Context> context)
{
    v8::HandleScope scope;

    // register the module in globale context
    v8::Local<v8::Object> global = context->Global();

    <CREATE_NAME_SPACES>
    
    <CREATE_CLASS_TEMPLATES>

    <ADD_CLASS_METHODS>

    <INHERITANCES>

    <REGISTER_CLASSES>
}

Namespaces

Namespaces are objects without class templates. I.e., instances are created, referenced locally, used as contexts for other registrations, and stored in the according parent contexts.

Create Class Template

    SWIGV8_$CLASSNAME = SWIGV8_CreateClassTemplate("$LOCAL_CLASSNAME" , $CLASSNAME_new);

• LOCAL_CLASSNAME: the class name without context, i.e., namespaces

Add Member Function

    SWIGV8_AddClassMethod(SWIGV8_$CLASSNAME, "$METHODNAME", $METHOD_WRAPPER);

• METHODNAME: the name of the function as in C++
• METHOD_WRAPPER: the name of the generated wrapper function TODO: specify different versions

Add Property

    SWIGV8_AddProperty(SWIGV8_$CLASSNAME, "$VARNAME", $GET_WRAPPER, $SET_WRAPPER);

• GET_WRAPPER: the name of the generated wrapper for the property getter
• SET_WRAPPER: the name of the generated wrapper for property setter; optional (i.e., maybe NULL)

Inheritance

    SWIGV8_$CLASSNAME->Inherit(SWIGV8_$SUPERCLASS);

• Note: multiple inheritance is not possible; thus we will always take the first parent class

Register class

    $CONTEXT->Set(v8::String::NewSymbol("$LOCAL_CLASSNAME"), SWIGV8_$CLASSNAME->GetFunction());

• Note: every class template has an associated ctor function wrapper, which is registered here
• CONTEXT: either global, or the according namespace instance

HELPER_FUNCTIONS

A lot of boiler-plate code can be shifted into static helper functions:

/**
 * Creates a class template for a class without extra initialization function. 
 */
v8::Persistent<v8::FunctionTemplate> SWIGV8_CreateClassTemplate(const char* symbol) {
    v8::Local<v8::FunctionTemplate> class_templ = v8::FunctionTemplate::New();
    class_templ->SetClassName(v8::String::NewSymbol(symbol));

    v8::Handle<v8::ObjectTemplate> inst_templ = class_templ->InstanceTemplate();
    inst_templ->SetInternalFieldCount(1);

    return v8::Persistent<v8::FunctionTemplate>::New(class_templ);
}

/**
 * Creates a class template for a class with specified initialization function. 
 */
v8::Persistent<v8::FunctionTemplate> SWIGV8_CreateClassTemplate(const char* symbol, v8::InvocationCallback _func) {
    v8::Local<v8::FunctionTemplate> class_templ = v8::FunctionTemplate::New(_func);
    class_templ->SetClassName(v8::String::NewSymbol(symbol));

    v8::Handle<v8::ObjectTemplate> inst_templ = class_templ->InstanceTemplate();
    inst_templ->SetInternalFieldCount(1);

    return v8::Persistent<v8::FunctionTemplate>::New(class_templ);
}

/**
 * Sets the pimpl data of a V8 class. 
 */
v8::Handle<v8::Value> V8GeneratorUtils::SetInstance(const v8::Arguments& args, void* data) {
    v8::HandleScope scope;

    v8::Handle<v8::Object> self = args.Holder();
    self->SetInternalField(0, v8::External::New(data));

    return self;
}

/**
 * Registers a class method with given name for a given class template. 
 */
void V8GeneratorUtils::AddClassMethod(v8::Handle<v8::FunctionTemplate> class_templ, const char* symbol, v8::InvocationCallback _func) {
    v8::Handle<v8::ObjectTemplate> proto_templ = class_templ->PrototypeTemplate();
    proto_templ->Set(v8::String::NewSymbol(symbol), v8::FunctionTemplate::New(_func));    
}

/**
 * Registers a class property with given name for a given class template. 
 */
void V8GeneratorUtils::AddProperty(v8::Handle<v8::FunctionTemplate> class_templ, const char* varname, v8::AccessorGetter getter, v8::AccessorSetter setter) {
    v8::Handle<v8::ObjectTemplate> proto_templ = class_templ->InstanceTemplate();
    proto_templ->SetAccessor(v8::String::New(varname), getter, setter);
}